1. Field of the Invention:
The present invention relates to improvements in a position detecting device and a position pointing device therefor, which employ electric waves.
2. Description of the Related Art:
Prior to the instant application, the applicant has proposed, in Japanese Patent Application No. 61-213970 (Japanese Patent Laid-Open No. 63-70326), a position detecting device in which a tablet exchanges electric wave signals with a position pointing device so as to determine the coordinate value of a position pointed by the position pointing device.
Briefly, the position detecting device disclosed in Japanese Patent Laid-Open No. 63-70326 has a plurality of loop coils constituting the tablet and is adapted to transmit an electric wave of a predetermined frequency. The electric wave is received by a resonance circuit provided in the position pointing device so that resonance takes place in the resonance circuit to emit electric wave. This electric wave is received by the loop coil so that a voltage is induced in the loop coil. This operation is conducted successively on the plurality of loop coils constituting the tablet, so that the coordinate value of the position pointed by the position pointing device is determined based on the levels of the voltages induced in the loop coils.
The position detecting device of the type described faces a demand for the ability to enter various kinds of information in addition to the coordinate value of a pointed position, such as information which indicates that the position pointing device, e.g., a pen or the like, has been set to a position for pointing a definite position (this state will be referred to as "pen-down state," hereinafter), information concerning the type of the position pointing device, e.g., a pen, a cursor or the like, as well as a demand for inputting, together with the coordinate values, information for continuously varying values of parameters other than the coordinate information, such as, for example, thickness or width of a line and hue or density (brightness) of the position or area appointed by the pointing device.
To cope with such demands, the position pointing device disclosed in Japanese Patent Laid-Open No. 63-70326 employs a manual switch which selectively connects, to the resonance circuit which is constituted by a coil and a capacitor, an additional capacitor so as to slightly vary the resonance frequency according to the operation of the switch, the slight change in the resonance frequency being detected as a variation in the phase angle with respect to the predetermined frequency so as to be used as information indicative of the aforesaid pen-down state or the type of the position pointing device.
In Japanese Patent Application No. 62-208293 (Japanese Patent Laid-Open No. 64-53223), the applicant also proposed a position detecting device having a resonance circuit including a coil the inductance of which continuously varies according to the pen pressure, so that the resonance frequency continuously varies according to the pen pressure, the linear variation in the resonance frequency being detected as a continuous variation in the phase angle with respect to the predetermined frequency so as to be used as information for continuously varying the parameter (hereinafter referred to as "continuous amount information").
The device disclosed in Japanese Patent Laid-Open No. 64-53223 sets the range over which the resonance frequency varies in accordance with the variation in the inductance of the coil so that it coincides with the range (about -60.degree. to about +60.degree.) over which such variation in the resonance frequency can be detected in terms of phase angle in relation to the predetermined frequency. This posed a problem in that only one type of continuous amount information can be entered.
To cope with the problem, the applicant proposed, in Japanese Patent Application No. 63-308712 (Japanese Patent Laid-Open No. 2-155019), a device which permits the input of two types of continuous amount information by setting the range over which the resonance frequency continuously varies in accordance with the pen pressure so that it can be switched between two ranges obtained by nearly bisecting the range over which such variation can be detected in terms of phase angle with respect to the predetermined frequency. The applicant further proposed, in Japanese Patent Application No. 4-36508, a device which is designed to selectively transmit a plurality of electric waves of different frequencies from a tablet and also selectively set the range over which the resonance frequency continuously varies with the pen pressure as a range over which such variation can be detected in terms of the phase angle corresponding to each of the plurality of different frequencies, thereby permitting the input of a plurality of continuous amount information.
The device disclosed in Japanese Patent Laid-Open No. 2-155019, however, was disadvantageous in that the varying range of the information that can be transmitted by a piece of continuous amount information is limited and also in that the phase angle for the same pen pressure completely changes when the range is changed, requiring separate correction values for correcting the continuous amount information with respect to the phase angles. Further, the device disclosed in Japanese Patent Application No. 4-36508 requires that a plurality of electric waves be set at different frequencies which are appropriately apart from each other so that the resonance frequencies do not overlap each other when they vary according to the pen pressure, presenting a disadvantage in that it needs a wider frequency domain.